Coal Trading Assets and Liabilities, Net, Fair Value Disclosure

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- Definition

Futures, Swaps And Options Fair Value Disclosure

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- Definition

Physical Purchase Sale Contracts Fair Value Disclosure

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- Definition

Quality, level 3 unobservable input as a percentage of overall valuation

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- Definition

Amount of unrealized (holding) gain (loss) which is included in the statement of income (or changes in net assets) related to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

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- Definition

Amount of gain (loss) recognized in the income statement of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19279-110258

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- Definition

Amount of transfers of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset) out of level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19279-110258

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- Definition

Fair value of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19279-110258

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Coal Trading - Fair Value (Details) - Coal Trading - USD ($) $ in Millions	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Apr. 01, 2017	Sep. 30, 2017	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Successor \| Fair Value, Measurements, Recurring
Fair value coal trading net assets (liabilities) measured on recurring basis:
Futures, swaps and options	$ (2.1)				$ (2.1)		$ (7.2)
Physical purchase/sale contracts	(7.2)				(7.2)		(1.9)
Total net financial assets (liabilities)	(9.3)				(9.3)		(9.1)
Successor \| Level 1 \| Fair Value, Measurements, Recurring
Fair value coal trading net assets (liabilities) measured on recurring basis:
Futures, swaps and options	0.0				0.0		(3.0)
Physical purchase/sale contracts	0.0				0.0		0.0
Total net financial assets (liabilities)	0.0				0.0		(3.0)
Successor \| Level 2 \| Fair Value, Measurements, Recurring
Fair value coal trading net assets (liabilities) measured on recurring basis:
Futures, swaps and options	(2.1)				(2.1)		(4.2)
Physical purchase/sale contracts	(5.5)				(5.5)		(1.9)
Total net financial assets (liabilities)	(7.6)				(7.6)		(6.1)
Successor \| Level 3
Fair value coal trading net assets (liabilities) measured on recurring basis:
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	(1.7)	$ 0.0	$ (0.7)	$ 0.0	(1.7)	$ 0.0	0.0	$ 0.0	$ (1.1)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers out of Level 3		0.0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	(1.7)	0.0			(1.7)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(1.7)	$ 0.0		0.0	(1.7)
Successor \| Level 3 \| Fair Value, Measurements, Recurring
Fair value coal trading net assets (liabilities) measured on recurring basis:
Futures, swaps and options	0.0				0.0		0.0
Physical purchase/sale contracts	(1.7)				(1.7)		0.0
Total net financial assets (liabilities)	(1.7)				(1.7)		$ 0.0
Predecessor \| Level 3
Fair value coal trading net assets (liabilities) measured on recurring basis:
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs			(0.7)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers out of Level 3	$ 0.0		0.0	0.7	$ 0.0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings			0.2	$ 0.0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)			$ 0.3
Minimum \| Successor
Fair value coal trading net assets (liabilities) measured on recurring basis:
Credit and non-performance risk, level 3 unobservable input as a percentage of overall valuation	(35.60%)				(35.60%)
Maximum \| Successor
Fair value coal trading net assets (liabilities) measured on recurring basis:
Credit and non-performance risk, level 3 unobservable input as a percentage of overall valuation	(36.00%)				(36.00%)
Weighted Average \| Successor
Fair value coal trading net assets (liabilities) measured on recurring basis:
Credit and non-performance risk, level 3 unobservable input as a percentage of overall valuation	(35.80%)				(35.80%)